Detecting Permanent Magnet Demagnetization in Wind Turbine Generators
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Solution Overview
Problem
Modern direct drive wind turbines with permanent magnet generators face challenges in detecting demagnetization of Neodymium Iron Boron (NdFeB) magnets due to temperature variations and aging, which affects the generator's magnetic flux and efficiency.
Innovation Solution
A method involving a frequency converter with voltage and temperature sensors to determine the generator's magnetic flux by disabling the AC/DC converter, measuring the generator output voltage and speed, compensating for temperature effects, and comparing flux density values to detect demagnetization events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If permanent magnet generators are used in wind turbines to achieve high efficiency and low weight, then generator performance is improved, but the risk of demagnetization due to temperature and aging increases
Solution Approach 1:
The system performs preliminary demagnetization detection by measuring back-EMF voltage and comparing it against predetermined thresholds before actual demagnetization occurs. This allows preventive maintenance actions to be taken, addressing the reliability concern while preserving the high efficiency benefit of permanent magnet generators.
Solution Approach 2:
The system continuously monitors generator output voltage and calculates magnetic flux to provide feedback on magnet health status. This feedback mechanism enables real-time detection of demagnetization trends, allowing the system to maintain reliability while operating permanent magnet generators at high efficiency.
2Reliability
If demagnetization detection methods are implemented to monitor magnet health, then reliability is improved, but device complexity increases
Solution Approach 1:
The system uses the generator's own output voltage and operational parameters to perform self-diagnosis of magnet health. By calculating back-EMF from existing measurements rather than requiring separate sensors or test equipment, the system achieves reliable demagnetization detection without adding significant complexity.
Solution Approach 2:
The detection system utilizes the existing frequency converter and voltage measurements already present in the wind turbine for other purposes. The same hardware infrastructure serves both power conversion and magnet health monitoring functions, avoiding additional complex detection equipment.
3Measurement precision
If temperature compensation is applied to account for reversible magnetic flux changes, then measurement precision is improved, but calculation complexity increases
Solution Approach 1:
The system compensates for temperature effects by adjusting the predetermined flux density threshold based on measured temperature and known temperature coefficients. This simple parameter adjustment improves measurement precision without requiring complex real-time calculations, as the temperature compensation is performed through lookup tables or straightforward arithmetic.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables cost-effective and efficient detection of demagnetization in wind turbine magnets, allowing for timely intervention and maintaining generator performance by determining magnetic flux changes caused by temperature and aging.
Implementation Method 1
the rotation of the rotor in relation to the stator generates the (generator) output voltage of the generator
Implementation Method 2
The remanent flux density Br of a Nedoymium Iron Boron (NdFeB) is influenced by the ambient temperature. The temperature coefficient a of the remanent flux density Br (also called magnetic output), i.e. how Br varies with temperature
Implementation Method 3
determine the generator output voltage by the voltage sensor of the frequency converter
Data Source
AI summary
The invention relates to a method to detect a decrease of the demagnetization of permanent magnets (32) of the generator (12) of a wind turbine (1), wherein a frequency converter (14) is able adapt the variable frequency (f1) of the generator output voltage (Vout) to the frequency (f2) of a power grid (19), wherein the AC/DC converter (13) or the DC/AC converter (16) of the frequency converter (14) is been disabled, the electrical connections (Vout) between the generator (12) and the frequency converter (14) are switched on via circuit breakers (17), the generator speed (ω) is determined; the generator output voltage (Vout) is determined by a voltage sensor (21) which is part of the frequency converter (14), the magnetic flux density (φ) of the generator (12) is calculated depending on the generator speed (ω) and the generator output voltage (Vout), a demagnetization event is determined by comparing the resulting flux density value (φres) with a predetermined flux density value (φref).